Papers by Author: Yun Jaie Choi

Abstract: The aim of this study is to prepare mucoadhesive chitosan microspheres for protein drug to deliver to intestine through oral administration. The thiolated Eudragit was synthesized by reaction between L-cysteine hydrochloride and Eudragit® L-100. About 8 mol-% of cysteine was introduced to the Eudragit-cysteine conjugate. The conjugate was used to coat bovine serum albumin (BSA)-loaded chitosan microspheres. The average particle sizes of BSA-loaded thiolated Eudragit-coated chitsoan microspheres (TECMs) were 4.06±0.74 .m and the uniform sizedistribution was shown. The in vitro release of BSA from BSA-loaded TECMs was pH-dependent. Our results indicated that thiolated Eudragit might be a good candidate as a coating material for oral delivery of protein drug owing to mucoadhesive and pH-sensitive properties.

Abstract: The objective of this study is to investigate whether the PEGylated conjugated linoleic acid (PCLA) as an anti-cancer prodrug can have favorable stability, biological activity, and prevention of proliferation in MCF-7 breast cancer cells for anti-cancer when compared with conjugated linoleic acid (CLA) itself. The CLA was simply coupled to poly(ethylene glycol) (PEG) at melting state without solvent or catalyst through ester linkage between carboxylic group of CLA and hydroxyl one of PEG. The results showed that the half life of PCLA was 55h in cell culture medium at pH 7.4 and 37°C. Apoptosis of MCF-7 breast cancer cells were induced by not only CLA- but PCLA-treatment with increasing concentrations whereas PCLA increased cell viability when compared with CLA itself. These results indicate that the PCLA is a more stable and valuable prodrug in that it has good stability and inhibition of cancer cell proliferation.

Abstract: The strategies developed for gene delivery are generally classified into two categories of viral and non-viral vectors. The limitation of viral vectors, which have problems including toxicity, immunogenicity and inflammatory response has led to the development of a novel, synthetic vectors based on non-viral vectors. Chitosan, one of non-viral vectors, has been a good candidate in gene delivery field. Moreover, galactosylated chitosan (GC) had the specific recognition of hepatocytes by galactose in the GC. Also, carbonate apatite increased the rate of DNA endocytosis and the efficiency of gene transfer. We describe here a new concept for improving cell specificity and transfection efficiency by hybridization of carbonate apatite (CAp) with GC. The complex formation was confirmed by agarose gel electrophoresis. The complex optimized through controlling calcium ion and charge ratio was evaluated on the cell specificity and transfection efficiency.

Abstract: Thiolated polymers have been studied by many researchers because of the mucoadhesive properties of thiol group. Alginate is a natural and biocompatible polymer that has been widely used in drug delivery. In this study, thiolated chitosan microspheres (TCMs) were prepared by ionic gelation process with tripolyphosphate and then, the bovine growth hormone (BGH) was loaded as a model drug. Finally, the BGH-loaded TCMs (BTCMs) were coated with alginate to improve the stability in gastrointestinal (GI) track. The alginate-coated BTCMs (ABTCMs) were observed as spherical shapes. The average particle sizes of ABTCMs were 6.97±0.55 -m and the sizedistribution was shown uniformly. Release of BGH from ABTCMs was decreased by coating with alginate and increased rapidly with the change in medium pH from 1.2 to 7.4. Results indicate that the ABTCMs have a potential as a drug carrier for oral drug delivery.

Abstract: In this study, novel polycaprolactone/hydroxyapatite (PCL/HA) scaffolds were prepared to increase mechanical properties and degradation of PCL/HA ones for bone tissue engineering. PCL macromers were synthesized through the reaction of PCL diol (Mn: 530, 1250, and 2000) and PCL triol (Mn: 900) with acryloyl chloride and confirmed using nuclear magnetic resonance spectrometer (NMR) and fourier transform infrared (FTIR). The PCL/HA scaffolds were prepared by cross-linking of PCL macromer in the presence of HA by UV treatment and freeze drying methods. Mechanical property and porosity as well as degradability of the PCL/HA scaffolds were also investigated. PCL/HA scaffolds showed faster degradation and higher compressive modulus than those of PCL itself due to their low crystallinity and modification of terminal groups. The pore morphology and pore sizes of the PCL/HA scaffold were checked by scanning electron microscope (SEM). Cell cytotoxicity and proliferation of MG-63 osteoblast cultured onto the PCL/HA scaffold was assessed by lactate dehydrogenase (LDH) assay and Alamar blue assay, respectively. The novel PCL/HA scaffold appears to be suitable for bone substitutes.

Abstract: The purpose of this study is to make use of trans10,cis12 CLA (t-CLA) that has potential for proliferation and differentiation to form adipocyte on the collagen-coated surface. Results provided evidences of good adhesion, growth, viability, and differentiation of adipocyte on collagen-coated surface compared with non-coated surface. Also, the results showed that mouse 3T3-L1 preadipocyte can be successfully and reproducibly cultured on the collagen-coated surface, and the adipocyte precursor cells placed on the collagen-coated surface are able to undergo full maturation into adipocytes in the control cells. Moreover, glycerol-3-phosphate dehydrogenase (GPDH) activity in 3T3-L1 preadipocyte cultured on collagen-coated surface with t-CLA was higher than that on polystyrene (PS) surface due to higher cell adhesion and cell viability. These results suggest that collagen coating may provide a promising approach to develop a new adipocyte replacement strategy using CLA.

Abstract: The development of an efficient targeted gene delivery system into cells is an important strategy for the advancement of gene therapy. The targeted gene delivery system is especially important in non-viral gene transfer which shows the relative low transfection efficiency. And it also opens the possibility of selective delivery of therapeutic plasmids to specific tissues. Chitosan has been considered to be a good candidate for gene delivery system, since it is already known as a biocompatible, biodegradable, and low toxic material with high cationic potential. However, low specificity and low transfection efficiency of chitosan need to be overcome prior to clinical trial. In this study, we focused on the chemical modification of chitosan for enhancement of cell specificity and transfection efficiency.